1. Field of the Invention
This invention relates to an additive composition for improving the cold flow properties of middle distillates such as diesel fuels and heating oils. More particularly, the invention relates to a diesel fuel composition having improved cold flow properties imparted by an additive composition comprising three or more components including (A) an oil-soluble ethylene backbone flow improving polymer, (B) a hydrocarbyl substituted amine salt and/or amide of a carboxylic acid or anhydride and (C) a hydrocarbyl substituted amine salt of a derivative of a phosphoric acid.
2. Description of the Prior Art
Serious problems have been encountered by heating oils and diesel and jet fuels that are subject to low temperatures. These petroleum products are frequently subjected to low temperatures below their pour point, resulting either in distribution or operating difficulties or both. For example, the distribution of heating oils by pumping or siphoning is rendered difficult or impossible at temperatures around or below the pour point of the oil. Similarly, the flow of fuels at such low temperatures cannot be maintained through filters, leading to the failure of equipment to operate.
It is, of course, well known to add pour depressants to middle distillates, such as heating oils and diesel fuels, to improve their cold flow properties. For example, various polymers, useful as middle distillate pour point depressants, prepared from ethylene have been described in the patent literature. These pour depressants include copolymers of ethylene and vinyl esters of lower fatty acids such as vinyl acetate (U.S. Pat. No. 3,048,479); copolymers of ethylene and alkyl acrylate (Canadian Patent No. 676,875); terpolymers of ethylene with vinyl esters and alkyl fumarates (U.S. Pat. Nos. 3,304,261 and 3,341,309); polymers of ethylene (British Patents Nos. 848,777 and 993,744); chlorinated polyethylene (Belgian Patent No. 707,371 and U.S. Pat. No. 3,337,313): etc.
Polymers having alkyl groups in the range of C.sub.6 to C.sub.18, such as homopolymers and copolymers of olefins, alkyl esters of unsaturated dicarboxylic acids (e.g., copolymers of dialkyl fumarate with vinyl acetate), and copolymers of olefins and said esters, are known in the art, principally as lube oil pour depressants and/or V.I. improvers. For example, U.S. Pat. No. 2,379,728 teaches olefin polymers as lube pour depressants; U.S. Pat. No. 2,460,035 shows polyfumarates; U.S. Pat. No. 2,936,300 shows a copolymer of dialkyl fumarate and vinyl acetate; while U.S. Pat. No. 2,542,542 teaches copolymers of olefins, such as octadecene with maleic anhydride esterified with alcohol, e.g., lauryl alcohol, in lube and heating oils.
Combinations of various pour depressants and flow improvers for middle distillates are also well known. For example, U.S. Pat. No. 4,153,422 describes a pour point depressing combination of ethylene vinyl ester copolymers with a polyester of a C.sub.14 to C.sub.16 substantially straight chained alkyl ester of an ethylenically unsaturated mono carboxylic acid.
U.K. Patent No. 1,469,016 teaches ethylene polymers or copolymers which are pour depressants for distillate fuels, in combination with a second polymer having alkyl groups of 6 to 18 carbon atoms, which is a polymer of an olefin or unsaturated dicarboxylic acid ester, useful in improving the cold flow properties of distillate fuel oils.
U.S. Pat. No. 3,982,909 teaches nitrogen compounds such as amides, diamides, ammonium salts or monoesters of dicarboxylic acids, alone or in combination with a hydrocarbon microcrystalline wax and/or a pour point depressant, particularly an ethylene backbone polymeric pour point depressant, are wax crystal modifiers and cold flow improvers for middle distillate fuel oils, particularly diesel fuel.
U.S. Pat. Nos. 3,444,082 and 3,846,093 teach various amides and salts of alkenyl succinic anhydride reacted with amines, in combination with ethylene copolymer pour point depressants, for distillate fuels.
U.S. Pat. Nos. 2,894,951 and 3,129,699 describe the use of heterocyclic polyamine salts of partial esters of phosphorodithioic acids of the formula (RO).sub.2 P(s)SH as additives to improve the ignition characteristics of diesel fuel.
Middle distillate fuel oils containing three or more additives for improvement of cold flow properties are also known. For example, U.S. Pat. No. 4,211,534 discloses a three component additive combination for distillate fuel oils comprising (A) an ethylene backbone distillate fuel oil pour depressant polymer, (B) a second polymer having alkyl side chains of 6 to 30 carbon atoms and derived from carboxylic acid ester or olefins, and (C) a nitrogen compound, e.g., amides and salts of a carboxylic acid or anhydride.